Method and device for controlling fluid flow in an optical assembly

ABSTRACT

An optical assembly ( 222 ) for directing and/or focusing a beam of light energy for an exposure apparatus ( 10 ) includes an optical housing ( 240 ) and one or more optical elements ( 242 ) that cooperate to form an optical cavity ( 270 ) having one or more stagnant flow areas ( 272 ). The optical assembly ( 222 ) also includes one or more flow diverters ( 246 ) for improving the flow a replacement fluid ( 250 ) in the stagnant flow areas ( 272 ) of the optical cavity ( 270 ) during purging of the optical assembly ( 222 ) with the replacement fluid ( 250 ).

FIELD OF THE INVENTION

[0001] The present invention is directed to an optical assembly for anexposure apparatus. More specifically, the present invention is directedto an optical assembly that can be efficiently purged and a method forefficiently purging an optical assembly.

BACKGROUND

[0002] Exposure apparatuses are commonly used to transfer an image froma reticle onto a semiconductor wafer. A typical exposure apparatusincludes an apparatus frame, an illumination source, a reticle stage, awafer stage, and an optical assembly that cooperate to transfer an imageof an integrated circuit from the reticle onto the semiconductor wafer.The illumination source generates a beam of light energy that passesthrough the reticle. The optical assembly directs and/or focuses thelight passing through the reticle to the wafer.

[0003] The sizes of the integrated circuits transferred onto the waferare extremely small. Accordingly, precise directing and/or focusing ofthe beam of light energy by the optical assembly is critical to themanufacture of high-density semiconductor wafers.

[0004] A typical optical assembly includes a tubular shaped housing andtwo or more spaced apart optical elements that are secured to theoptical housing. Unfortunately, depending upon the wavelength of lightenergy generated by the illumination source, the type of fluid in thelight path, including between the optical elements, can greatlyinfluence the performance of the exposure apparatus. Typically, opticalassemblies have air between the optical elements. Air is a gaseousmixture that is approximately twenty-one percent oxygen. Somewavelengths of light energy are absorbed by oxygen. Air also includeswater vapor, carbon dioxide and other hydrocarbons, which also absorbsignificant amounts of the light energy within certain wavelengthranges. Even trace amounts of these unwanted fluids, i.e. ten parts permillion or less, can result in significant absorption of the lightenergy. Absorption of the light energy can lead to losses of intensityand uniformity of the light energy. Moreover, absorption of the lightenergy can lead to localized heating within the optical assembly. Thus,air within the optical assembly can adversely influence the performanceand accuracy of the exposure apparatus. As a consequence, the quality ofthe integrated circuits formed on the wafer can be adversely influenced.

[0005] One solution includes sealing the optical elements to the opticalhousing to form a sealed optical cavity, and replacing the air in theoptical cavity with a weakly absorbing, replacement fluid. Thereplacement process can include directing the replacement fluid into aninlet of the optical cavity while allowing the air to be pushed from anoutlet of the optical cavity. This process is continued until the amountof air in the optical cavity is reduced to an acceptable level.

[0006] Unfortunately, the sealed optical cavity can include one or morestagnant flow areas that are not readily purged. Stagnant flow areasexperience relatively low or non-existent fluid flow during the normalpurging process. These stagnant flow areas are particularly problematicif located in the light path. As a result thereof, a relatively largeamount of time and replacement fluid is required to purge the opticalcavity.

[0007] In light of the above, there is a need for an optical assemblythat is purged of any unwanted fluid relatively easily and efficiently.Moreover, there is a need for an optical assembly that minimizes theamount of time required to dilute the unwanted fluid and the amount ofreplacement fluid used to dilute the unwanted fluid in the opticalassembly to acceptable levels. Additionally, there is a need for anexposure apparatus that is capable of generating high-resolutionpatterns on a semiconductor wafer.

SUMMARY

[0008] The present invention is directed to an optical assembly fordirecting and/or focusing a beam of light energy. The optical assemblyincludes an optical housing and one or more optical elements thatcooperate to define an optical cavity that includes one or more stagnantflow areas. Additionally, the optical assembly includes an outlet port,an inlet port, and a flow diverter for purging the optical chamber. Afluid source directs a replacement fluid into the optical cavity throughthe inlet port and out the outlet port.

[0009] The flow diverter diverts and redirects the flow of thereplacement fluid in the optical cavity so that at least a portion ofthe replacement fluid is directed into the stagnant flow areas in theoptical cavity. This improves the flow of the replacement fluid in thestagnant flow areas, improves mixing of the fluids, minimizes the timeneeded to purge the optical assembly and the amount of replacement fluidused to dilute the unwanted fluid in the optical cavity to acceptablelevels.

[0010] In one embodiment, the optical assembly includes a plurality offlow diverters that are positioned at various strategic locations aroundthe optical housing to increate flow velocities in the stagnant flowareas and fluid mixing within the optical cavity. For example, one ofthe flow diverters can be positioned near each stagnant flow area. Inanother embodiment, one of the flow diverters can be positioned neareach stagnant flow area located in the light path.

[0011] The flow diverters assist in creating and controlling the flowpatterns of the replacement fluid in the optical cavity. Further, theflow diverters increase fluid flow in the stagnant flow areas. Forexample, flow diverters can be positioned near each optical element toexhaust the unwanted fluid in the tight spaces near each opticalelement. In one embodiment, the flow diverter is positioned outside theoptical path but in the fluid flow path. The flow diverters reduce theamount of trapped fluids and reduce the amount of dilution time requiredto replace the unwanted fluid with the replacement fluid.

[0012] In one embodiment, the flow diverter is a vane. In anotherembodiment, the flow diverter is a fan. The fan can be turned off and onat certain times so that possible vibration from the fan does notadversely influence optical performance. In another embodiment, the flowdiverter is an integral part of an element mount that retains theoptical element to the optical housing.

[0013] The present invention is also directed to an optical assembly, anexposure apparatus, a device and semiconductor wafer. Moreover, thepresent invention is also directed to a method for making an opticalassembly, an exposure apparatus, a device, and a semiconductor wafer.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The novel features of this invention, as well as the inventionitself, both as to its structure and its operation, will be bestunderstood from the accompanying drawings, taken in conjunction with theaccompanying description, in which similar reference characters refer tosimilar parts, and in which:

[0015]FIG. 1 is a schematic view of an exposure apparatus havingfeatures of the present invention;

[0016]FIG. 2A is a perspective view of an optical assembly and a purgingassembly having features of the present invention;

[0017]FIG. 2B is a cut-away view taken on line 2B-2B in FIG. 2A;

[0018]FIG. 2C is a perspective view of a flow diverter having featuresof the present invention;

[0019]FIG. 3 is a cut away view of another embodiment of the opticalassembly including a plurality of flow diverters;

[0020]FIG. 4A is a cut view of still another embodiment of the opticalassembly including a plurality of flow diverters;

[0021]FIG. 4B is a perspective view of five of the flow diverters ofFIG. 4A;

[0022]FIG. 5 is a cut away view of yet another embodiment of the opticalassembly including a plurality of flow diverters;

[0023]FIG. 6A is a flow chart that outlines a process for manufacturinga device in accordance with the present invention; and

[0024]FIG. 6B is a flow chart that outlines device processing in moredetail.

DESCRIPTION

[0025]FIG. 1 is a schematic view that illustrates a precision assembly,namely an exposure apparatus 10. The exposure apparatus 10 isparticularly useful as a lithographic device that transfers a pattern(not shown) of an integrated circuit from a reticle 12 onto a device,such as a semiconductor wafer 14. In FIG. 1, the exposure apparatus 10includes an apparatus frame 16, an illumination system 18 (irradiationapparatus), a reticle stage assembly 20, an optical assembly 22 (lensassembly), a wafer stage assembly 24, a control system 26, and ameasurement system 28. The exposure apparatus 10 mounts to a mountingbase 30, e.g., the ground, a base, or floor or some other supportingstructure. The design of the components of the exposure apparatus 10 canbe varied to suit the design requirements of the exposure apparatus 10.

[0026] As provided in detail below, the optical assembly 22 is designedso that the optical assembly 22 can be purged relatively efficiently.

[0027] A number of Figures include an orientation system thatillustrates an X axis, a Y axis that is orthogonal to the X axis and a Zaxis that is orthogonal to both X and Y axes. It should be noted thatthese axes can also be referred to as the first, second and third axes.

[0028] There are a number of different types of lithographic devices.For example, the exposure apparatus 10 can be used as scanning typephotolithography system that exposes the pattern from the reticle 12onto the wafer 14 with the reticle 12 and the wafer 14 movingsynchronously. In a scanning type lithographic device, the reticle 12 ismoved perpendicular to an optical axis of the optical assembly 22 by thereticle stage assembly 20 and the wafer 14 is moved perpendicularly tothe optical axis of the optical assembly 22 by the wafer stage assembly24. Scanning of the reticle 12 and the wafer 14 occurs while the reticle12 and the wafer 14 are moving synchronously.

[0029] Alternatively, the exposure apparatus 10 can be a step-and-repeattype photolithography system that exposes the reticle 12 while thereticle 12 and the wafer 14 are stationary. In the step and repeatprocess, the wafer 14 is in a constant position relative to the reticle12 and the optical assembly 22 during the exposure of an individualfield. Subsequently, between consecutive exposure steps, the wafer 14 isconsecutively moved with the wafer stage assembly 24 perpendicular tothe optical axis of the optical assembly 22 so that the next field ofthe wafer 14 is brought into position relative to the optical assembly22 and the reticle 12 for exposure. Following this process, the imageson the reticle 12 are sequentially exposed onto the fields of the wafer14 so that the next field of the wafer 14 is brought into positionrelative to the optical assembly 22 and the reticle 12.

[0030] However, the use of the exposure apparatus 10 provided herein isnot limited to a photolithography system for semiconductormanufacturing. The exposure apparatus 10, for example, can be used as anLCD photolithography system that exposes a liquid crystal display devicepattern onto a rectangular glass plate or a photolithography system formanufacturing a thin film magnetic head. Further, the present inventioncan also be applied to a proximity photolithography system that exposesa mask pattern from a mask to a substrate with the mask located close tothe substrate, without the use of a lens assembly.

[0031] The apparatus frame 16 is rigid and supports the components ofthe exposure apparatus 10. The apparatus frame 16 illustrated in FIG. 1supports the optical assembly 22, the illumination system 18, and thestage assemblies 20, 24 above the mounting base 30.

[0032] The illumination system 18 includes an illumination source 32 andan illumination optical assembly 34. The illumination source 32 emits abeam (irradiation) of light energy. The illumination optical assembly 34guides the beam of light energy from the illumination source 32 to theoptical assembly 22. The beam selectively illuminates different portionsof the reticle 12 and exposes the semiconductor wafer 14. In FIG. 1, theillumination source 32 is illustrated as being supported above thereticle stage assembly 20. Typically, however, the illumination source32 is secured to one of the sides of the apparatus frame 16 and theenergy beam from the illumination source 32 is directed to the reticle12 with the illumination optical assembly 34.

[0033] The illumination source 32 can be a g-line source having awavelength of approximately 436 nm, an i-line source having a wavelengthof approximately 365 nm, a KrF excimer laser having a wavelength ofapproximately 248 nm, an ArF excimer laser having a wavelength ofapproximately 193 nm or a F₂ laser having a wavelength of approximately157 nm. Alternatively, the illumination source 32 can generate chargedparticle beams such as an x-ray or electron beam. For instance, in thecase where an electron beam is generated, thermionic emission typelanthanum hexaboride (LaB₆) or tantalum (Ta) can be used as the cathodefor an electron gun. Furthermore, in the case where an electron beam isgenerated, the structure could be such that either a mask is used or apattern can be directly formed on a substrate without the use of a mask.

[0034] The optical assembly 22 projects and/or focuses the light passingthrough the reticle 12 to the wafer 14. In FIG. 1, dashed lines 35illustrate a representative example of the optical path that may beoccupied by the light passing through the optical assembly 22.

[0035] When far ultra-violet rays such as the excimer laser is utilized,glass materials such as quartz and fluorite that transmit farultra-violet rays can be used in the optical assembly 22. When the F₂type laser or x-ray is utilized, the optical assembly 22 can be eithercatadioptric or refractive, and when an electron beam is utilized,electron optics can consist of electron lenses and deflectors.

[0036] Also, with an exposure device that employs vacuum ultra-violetradiation (VUV) of wavelength 200 nm or shorter, use of the catadioptrictype optical system can be considered. Examples of the catadioptric typeof optical system include the disclosure Japan Patent ApplicationDisclosure No.8-171054 published in the Official Gazette for Laid-OpenPatent Applications and its counterpart U.S. Pat. No. 5,668,672, as wellas Japan Patent Application Disclosure No.10-20195 and its counterpartU.S. Pat. No. 5,835,275. In these cases, the reflecting optical devicecan be a catadioptric optical system incorporating a beam splitter andconcave mirror. Japan Patent Application Disclosure No.8-334695published in the Official Gazette for Laid-Open Patent Applications andits counterpart U.S. Pat. No. 5,689,377 as well as Japan PatentApplication Disclosure No.10-3039 and its counterpart U.S. patentapplication No. 873,605 (Application Date: Jun. 12, 1997) also use areflecting-refracting type of optical system incorporating a concavemirror, etc., but without a beam splitter, and can also be employed withthis invention. As far as is permitted, the disclosures in theabove-mentioned U.S. patents, as well as the Japan patent applicationspublished in the Official Gazette for Laid-Open Patent Applications areincorporated herein by reference.

[0037] The reticle stage assembly 20 holds and positions the reticle 12relative to the optical assembly 22 and the wafer 14. Similarly, thewafer stage assembly 24 holds and positions the wafer 14 with respect tothe projected image of the illuminated portions of the reticle 12 in theoperational position 34. The wafer stage assembly 24 is described inmore detail below.

[0038] Further, in photolithography systems, when linear motors (seeU.S. Pat. Nos. 5,623,853 or 5,528,118) are used in a wafer stage or amask stage, the linear motors can be either an air levitation typeemploying air bearings or a magnetic levitation type using Lorentz forceor reactance force. Additionally, the stage could move along a guide, orit could be a guideless type stage that uses no guide. As far as ispermitted, the disclosures in U.S. Pat. Nos. 5,623,853 and 5,528,118 areincorporated herein by reference.

[0039] Alternatively, one of the stages could be driven by a planarmotor, which drives the stage by an electromagnetic force generated by amagnet unit having two-dimensionally arranged magnets and an armaturecoil unit having two-dimensionally arranged coils in facing positions.With this type of driving system, either the magnet unit or the armaturecoil unit is connected to the stage and the other unit is mounted on themoving plane side of the stage.

[0040] Movement of the stages as described above generates reactionforces that can affect performance of the photolithography system.Reaction forces generated by the wafer (substrate) stage motion can bemechanically transferred to the floor (ground) by use of a frame memberas described in U.S. Pat. 5,528,100 and published Japanese PatentApplication Disclosure No. 8-136475. Additionally, reaction forcesgenerated by the reticle (mask) stage motion can be mechanicallytransferred to the floor (ground) by use of a frame member as describedin U.S. Pat. No. 5,874,820 and published Japanese Patent ApplicationDisclosure No. 8-330224. As far as is permitted, the disclosures in U.S.Pat. Nos. 5,528,100 and 5,874,820 and Japanese Patent ApplicationDisclosure No. 8-330224 are incorporated herein by reference.

[0041] The control system 26 receives information from the measurementsystem 28 and controls the stage mover assemblies 20, 24 to preciselyposition the reticle 12 and the wafer 14.

[0042] The measurement system 28 monitors movement of the reticle 12 andthe wafer 14 relative to the optical assembly 22 or some otherreference. With this information, the control system 26 can control thereticle stage assembly 20 to precisely position the reticle 12 and thewafer stage assembly 24 to precisely position the wafer 14. For example,the measurement system 28 can utilize multiple laser interferometers,encoders, and/or other measuring devices.

[0043] A photolithography system (an exposure apparatus) according tothe embodiments described herein can be built by assembling varioussubsystems, including each element listed in the appended claims, insuch a manner that prescribed mechanical accuracy, electrical accuracy,and optical accuracy are maintained. In order to maintain the variousaccuracies, prior to and following assembly, every optical system isadjusted to achieve its optical accuracy. Similarly, every mechanicalsystem and every electrical system are adjusted to achieve theirrespective mechanical and electrical accuracies. The process ofassembling each subsystem into a photolithography system includesmechanical interfaces, electrical circuit wiring connections and airpressure plumbing connections between each subsystem. Needless to say,there is also a process where each subsystem is assembled prior toassembling a photolithography system from the various subsystems. Once aphotolithography system is assembled using the various subsystems, acomprehensive adjustment is performed to make sure that accuracy ismaintained in the complete photolithography system. Additionally, it isdesirable to manufacture an exposure system in a clean room where thetemperature and cleanliness are controlled.

[0044]FIG. 2A is a perspective view of a combination 236 including anoptical assembly 222 and a fluid purging assembly 238 that is useful aspart of the exposure apparatus 10 (illustrated in FIG. 1). Alternately,the combination 236 can be used in other systems. The design of theoptical assembly 222 can be varied according to its design requirements.For example, the optical assembly 222 can magnify or reduce an imagefrom the reticle 12 (illustrated in FIG. 1). The optical assembly 222need not be limited to a magnification or a reduction system. Theoptical assembly 222 could also be a 1× system.

[0045]FIG. 2B is a cut-away view of the combination 236 of FIG. 2A. InFIG. 2B, the optical assembly 222 includes an optical housing 240, oneor more optical elements 242, one or more element retainers 244 thatsecure the optical elements 242 to the optical housing 240 and one ormore flow diverters 246. Further, the fluid purging assembly 238includes a fluid source 248 that provides a replacement fluid 250(illustrated as triangles) to the optical assembly 222. The design ofeach of these components can be varied to suit the design requirementsof the optical assembly 222. Dashed lines 235 illustrate arepresentative example of the optical path that may be occupied by thelight passing through the optical assembly 222.

[0046] In FIG. 2B, the optical housing 240 is substantially tubular orannular shaped and includes an inner wall 252 and an outer wall 254. Theouter wall 254 includes an annular shaped support flange 256 forsecuring the optical assembly 222 to the apparatus frame 16 (illustratedin FIG. 1). Alternatively, for example, the optical housing 240 caninclude a plurality of support flanges 256 for securing the opticalassembly 222 to the apparatus frame 16. In FIG. 2B, the optical housing240 is illustrated as a unitary structure. Alternatively, the opticalhousing 240 can have a different shape or can be divided into aplurality of annular or arch shaped sections that are assembled togetherto facilitate assembly of the optical elements 242 to the opticalhousing 240.

[0047] Additionally, the optical housing 240 includes one or more inletports 258 and one or more outlet ports 260 that are in fluidcommunication with the fluid purging assembly 238 for purging theoptical assembly 222. In FIG. 2B, the inlet port 258 extends through oneof the element mounts 244 and the outlet port 260 extends through theoptical housing 240. The number and exact location of the ports 258, 260can be varied according to the design of the optical assembly 222. InFIG. 2B, the optical assembly 22 includes a single inlet port 258positioned near the top of the optical housing 240 and a single outletport 260 positioned near the bottom of the optical housing 240.Alternatively, the ports 258, 260 can be switched or the optical housing240 can include a plurality of inlet ports 258 that are axially orradially spaced apart at strategic locations and a plurality of outletports 260 that are axially or radially spaced apart at strategiclocations to maximize flow velocities and fluid mixing of thereplacement fluid 250 with any unwanted fluid 262 (illustrated ascircles) in the optical assembly 222. The outlet ports 260 arepositioned to efficiently exhaust the unwanted fluid 262 from theoptical assembly 222.

[0048] The ports 258, 260 can also designed and positioned to assist increating and controlling the flow patterns of the replacement fluid 250in the optical assembly 222. The size of each port 258, 260 can bevaried. For example, each port 258, 260 has an inner diameter of betweenapproximately 3 and 50 millimeters.

[0049] The number of optical elements 242 utilized and the design ofeach optical element 242 can be varied to suit the requirements of theoptical assembly 222. In FIG. 2B, the optical assembly 222 includesseven, optical elements 242 that are spaced apart along an optical axis264, namely a first optical element 242A, a second optical element 242B,a third optical element 242C, a fourth optical element 242D, a fifthoptical element 242E, a sixth optical element 242F, and a seventhoptical element 242G. Alternately, the optical assembly 222 can includemore than seven or less than seven optical elements 242.

[0050] In FIG. 2B, each optical element 242 is generally disk shaped andincludes a front surface 266 and an opposed rear surface 268. The figureof at least one of the surfaces 266, 268 of each optical element 242 iscurved so that the light rays converge or diverge. In one embodiment,each optical element 242 is a refractive element. In this embodiment,each optical element 242 is made of a ground or molded substantiallytransparent material such as piece of glass or plastic. Alternatively,each optical element 242 can be a prism or a mirror.

[0051] Each optical element 242 can include one or more circulationchannels (not shown) that extend through the optical element 242 forcooling. The circulation channels can be positioned so that acirculating fluid can be circulated relatively evenly throughout theoptical element 242.

[0052] The element mounts 244 secure the optical elements 242 to theoptical housing 240. The design and number of element mounts 244 canvary. In the embodiment illustrated in FIG. 2B, the optical assembly 222includes seven element mounts 244 that are spaced apart along theoptical axis 264, namely a first element mount 244A that secures andseals the first optical element 242A to the optical housing 240, asecond element mount 244B that secures the second optical element 242Bto the optical housing 240, a third element mount 244C that secures thethird optical element 242C to the optical housing 240, a fourth elementmount 244D that secures the fourth optical element 242D to the opticalhousing 240, a fifth element mount 244E that secures the fifth opticalelement 242E to the optical housing 240, a sixth element mount 244F thatsecures the sixth optical element 242F to the optical housing 240, and aseventh element mount 244G that secures and seals the seventh opticalelement 242G to the optical housing 240. Alternatively, the opticalassembly 222 can include more than seven or less than seven elementmounts 244.

[0053] The first element mount 244A is somewhat flat ring shaped andextends between the inner wall 252 of the optical housing 240 and thefirst optical element 242A. Further, the first element mount 244Aencircles the first optical element 242A and seals the first opticalelement 242A to the optical housing 240. Somewhat similarly, the seventhelement mount 244G is somewhat flat ring shaped and extends between theinner wall 252 of the optical housing 240 and the seventh opticalelement 242G. Further, the seventh element mount 244G encircles theseventh optical element 242G and seals the seventh optical element 242Gto the optical housing 240.

[0054] In contrast, (i) the second element mount 244B includes aplurality of spaced apart, radially extending spokes that secure thesecond optical element 242B to the optical housing 240, (ii) the thirdelement mount 244C includes a plurality of spaced apart, radiallyextending spokes that secure the third optical element 242C to theoptical housing 240, (iii) the fourth element mount 244D includes aplurality of spaced apart, radially extending spokes that secure thefourth optical element 242D to the optical housing 240, (iv) the fifthelement mount 244E includes a plurality of spaced apart, radiallyextending spokes that secure the fifth optical element 242F to theoptical housing 240, and (v) the sixth element mount 244F that includesa plurality of spaced apart, radially extending spokes that secure thesixth optical element 242F to the optical housing 240. For example, eachof the element mounts 244B-244F can include six spokes, more than sixspokes or less than six spokes.

[0055] Each element mount 244 can be made of a number of materialsincluding metal, plastic or other suitable material.

[0056] The optical housing 240, the optical elements 242, and theelement mounts 244 cooperate to define one or more sealed opticalcavities 270. In FIG. 2B, these elements cooperate to define a singleoptical cavity 270 that is substantially right, cylindrical shaped andhas a circular shaped cross-section. However, other shapes are alsopossible.

[0057] Additionally, the optical assembly 222 can include one or morestagnant flow areas 272 (illustrated as a dashed box). Stagnant flowareas 272 experience low or non-existent flow during purging without theflow diverters 246. For example, in FIG. 2B, the optical assembly 222can include a stagnant flow area 272 between each pair of adjacentoptical elements 242. More specifically, the optical assembly 222includes (i) a first stagnant flow area 272A between the first opticalelement 242A and the second optical element 242B, (ii) a second stagnantflow area 272B between the second optical element 242B and the thirdoptical element 242C, (iii) a third stagnant flow area 272C between thethird optical element 242C and the fourth optical element 242D, (iv) afourth stagnant flow area 272D between the fourth optical element 242Dand the fifth optical element 242E, (v) a fifth stagnant flow area 272Ebetween the fifth optical element 242E and the sixth optical element242F, and (vi) a sixth stagnant flow area 272F between the sixth opticalelement 242F and the seventh optical element 242G.

[0058] In FIG. 2B, each of the stagnant flow areas 272 is between a pairof adjacent optical elements 242. Alternatively, two or more stagnantflow areas 272 can be located between adjacent optical elements 242.Further, in FIG. 2B, each stagnant flow area 272 is substantially in theoptical path 235. Alternatively, stagnant flow areas 272 can be anywherein the optical cavity 270. For example, bolts or other structures can bethe location of stagnant flow areas 272. Further, these stagnant flowareas 272 can be outside the optical path 235.

[0059] The one or more flow diverters 246 facilitate the efficientpurging of the optical assembly 222 with the replacement fluid 250. Morespecifically, the flow diverters 246 divert and/or increase the flow ofthe replacement fluid 250 in the stagnant flow areas 272 to improve theflow of the replacement fluid 250 in the optical cavity 270 withoutincreasing the overall flow of the replacement fluid 250 in the opticalassembly 222.

[0060] The number of the flow diverters 246 can be varied depending uponthe design of the optical assembly 222. For example, FIG. 2B illustratesthat the optical assembly 222 includes six flow diverters 246, namely afirst flow diverter 246A positioned between the first optical element242A and second optical element 242B, a spaced apart second flowdiverter 246B positioned between the second optical element 242B and thethird optical element 242C, a spaced apart third flow diverter 246Cpositioned between the third optical element 242C and the fourth opticalelement 242D, a spaced apart fourth flow diverter 246D positionedbetween the fourth optical element 242D and the fifth optical element242E, a fifth flow diverter 246E positioned between the fifth opticalelement 242E and the sixth optical element 242F, and a sixth flowdiverter 246F positioned between the sixth optical element 242F and theseventh optical element 242G.

[0061] Alternatively, the optical assembly 222 can include more than sixor less than six flow diverters 246.

[0062] In FIG. 2B, the flow diverters 246 are positioned outside theoptical path 235 but in the flow path of the replacement fluid 250.Alternatively, the flow diverters 246 can be positioned within theoptical path 235 during purging of the optical assembly 232 and moved byone or more actuators (not shown) out of the optical path 235 duringprocessing of the wafer 14.

[0063] The design of each flow diverters 246 can be varied dependingupon the design of the optical assembly 222. For example, one or more ofthe flow diverters 246 can include a vane, e.g. a deflector thatredirects, deviates or bends the flow of the replacement fluid 250 inthe optical cavity 270.

[0064] The fluid purging assembly 238 purges and replaces some or all ofthe unwanted fluid mixture 262 in the optical cavity 270 with thereplacement fluid 250 until the level of unwanted fluid 262 in theoptical cavity 270 is reduced to acceptable levels. The design of thefluid purging assembly 238 can be varied to suit the purging requirementof the optical assembly 222. In FIG. 2B, the fluid purging assembly 238includes the fluid source 248 and a recovery system 274.

[0065] The fluid source 248 provides a source of pressurized replacementfluid 250 and directs the replacement fluid 250 into the inlet port(s)258 for purging the optical cavity 270. The design of the fluid source248 can be varied. For example, the fluid source 248 can be apressurized container retaining the replacement fluid 250 that is influid communication with the inlet port(s) 258. Alternatively, forexample, the fluid source 248 can include a fluid reservoir (not shown)and a fluid pump (not shown) that is in fluid communication with theinlet port(s) 258.

[0066] The fluid source 248 can include a manifold (not shown) that isin fluid communication with one or more of the inlet ports 258 anddirects the replacement fluid 250 to the desired inlet port 258.Additionally, the fluid source 248 can include one or more fluid valves(not shown) that are controlled with the control system 26 (illustratedin FIG. 1) to control the flow rate of the replacement fluid 250 in theoptical cavity 270. With this design, the control system 26 controls theopening and closing of each valve to create the desired flow of fluid inthe optical cavity 270.

[0067] The type of replacement fluid 250 can vary according to the typeof illumination system 18 (illustrated in FIG. 1) utilized. For example,the replacement fluid 250 can be a weakly absorbing gas or gas mixtureto minimize absorption of light energy and localized heating within theoptical assembly 222. Suitable replacement fluids 250 include inertgases such as helium, argon or neon. Inert gases, as examples, absorbfar less radiation than fluids sought to be purged from the opticalassembly 222 such as oxygen, water, carbon dioxide and otherhydrocarbons. Nitrogen may also serve as the replacement fluid 250 forsome radiation source wavelengths.

[0068] The recovery system 274 recovers and captures the unwanted gasmixture 262 that exhausts from the outlet ports 260 for recycling orproper handling. Alternately, the unwanted gas mixture 262 that exhaustsfrom the outlet ports 260 can be released directly in the atmosphere.

[0069]FIG. 2B illustrates the flow 276 (represented by arrows) of atleast a portion of the replacement fluid 256 in the optical cavity 270.More specifically, FIG. 2B illustrates that the flow diverters 246 arestrategically located within the optical assembly 222 to redirect atleast a portion of the replacement fluid 250 into the stagnant flowareas 272 and/or into the optical path 235. In particular, in FIG. 2B,(i) the replacement fluid 250 is released into the optical cavity 270near the first optical element 242A, (ii) next, the first flow diverter246A directs at least a portion of the replacement fluid 250 into thefirst stagnant flow area 272A, (iii) next, the second flow diverter 246Bdirects at least a portion of the replacement fluid 250 into the secondstagnant flow area 272B, (iv) next, the third flow diverter 246C directsat least a portion of the replacement fluid 250 into the third stagnantflow area 272C, (v) next, the fourth flow diverter 246D directs at leasta portion of the replacement fluid 250 into the fourth stagnant flowarea 272D, (vi) next, the fifth flow diverter 246E directs at least aportion of the replacement fluid 250 into the fifth stagnant flow area272E, (vii) next, the sixth flow diverter 246F directs at least aportion of the replacement fluid 250 into the sixth stagnant flow area272F, and (viii) finally, the replacement fluid 250 is forced out theoutlet port 260 and recovered by the recovery system 274.

[0070] It should be noted that in FIG. 2B, the flow diverters 246 causeflow 276 to be a somewhat serpentine shaped pattern in the opticalcavity 270 around the optical elements 242. Alternatively, the flowdiverters 246 can cause a different flow pattern.

[0071] The placement of the flow diverters 246 causes turbulence andimproves mixing of the fluids in the optical cavity 270, reduces thetime required to purge the optical assembly 222 and the amount ofreplacement fluid 250 used to dilute the unwanted fluid 262 in theoptical cavity 270 to acceptable levels is minimized.

[0072] The fluid purging assembly 238 can also include a fluid analyzer278 for detecting the composition of fluid exiting the optical cavity270. The fluid analyzer 278 can discern whether unwanted gases 262 arepresent in amounts that may cause undesirable effects during use of theoptical assembly 222. In one embodiment, the fluid analyzer 278indicates when the percentage of oxygen, water vapor, carbon dioxide orother hydrocarbons, as examples, is acceptable or excessive. Statedanother way, the fluid analyzer 278 can indicate when levels of theunwanted fluid 262 have decreased sufficiently to allow for properfunctioning of the optical assembly 222. An acceptable level as providedherein can be approximately less than 10 parts per million (ppm), orapproximately less than approximately one ppm, of the unwanted fluid262. Examples of constituents of the unwanted fluid 262 which can causeundesirable effects include oxygen, water and water vapor, carbondioxide, and other hydrocarbons. Thus, an acceptable level as providedherein may be approximately single digit, parts per million (ppm)residual oxygen level, residual water level, residual carbon dioxidelevel, or residual hydrocarbon level, although lower levels of theunwanted fluid 262 can be achieved with the present invention.

[0073] It should be noted that the fluid purging assembly 238 cancontinuously supply the replacement fluid 250 to the optical cavity 270.For example, the fluid source 248 can supply the replacement fluid 250at between approximately 10 liters per minute to 30 liters per minutefor between approximately 15 minutes to 60 minutes to initially purgethe optical cavity 270. Further, the fluid source 248 can supply thereplacement fluid 250 at between approximately ½ liter per minute to 10liters per minute to continuously purge the optical cavity 270 tomaintain the unwanted fluid 262 below the acceptable level.

[0074]FIG. 2C illustrates a perspective view of a vane 280 that can beused as a flow diverter 246 in the optical assembly 222 of FIG. 2B. Inthis embodiment, the vane 280 is a thin rigid, material that includes acurved surface 282 that redirects, bends and/or deviates the flow of thereplacement fluid 250 (illustrated in FIG. 2B). More specifically, thevane 280 includes a front side 284 that is curved, a rear side 286 thatis curved, a top surface 288 that is curved and has a radius that isapproximately equal to the radius of the inner wall 252 of the opticalhousing 240 (illustrated in FIG. 2B), a bottom surface 290 that iscurved and has a radius that is approximately equal to the radius of theinner wall 252 of the optical housing 240. The shape and dimensions ofthe curves can be varied to adjust the flow and to fit the opticalhousing 240.

[0075] However, the vane 280 can have an alternative shape and size. Thevane 280 can be made of a number of materials. Suitable materialsinclude metal, plastic, or a ceramic material. Further, each flowdiverter 246 can include more than one vane 280 that is spaced apartcircumferentially or along the optical axis 264 (illustrated in FIG.2B).

[0076]FIG. 3 is a cross-sectional view of another embodiment of acombination 336 including an optical assembly 322 and a fluid purgingassembly 338 that are somewhat similar to the corresponding componentsdescribed above. The optical assembly 322 includes optical elements342A-342G, element mounts 344A-344G, and flow diverters 346A-346F.Further, the optical assembly 322 includes stagnant flow areas372A-372F. However, in this embodiment, each of the flow diverters346A-346F is a fan 392 for directing flow into the stagnant flow areas372A-372F.

[0077] The design of each fan 392 can vary. In FIG. 3, each fan 392includes one or more thin rigid vanes 394, an output shaft 395 securedto the vanes 394, and an electric motor 396 that rotates the outputshaft 395 and the vanes 394. The electric fans 392 can be positioned topush the replacement fluid 350 into the stagnant flow areas 372A-372F ordraw replacement fluid 350 from the stagnant flow areas 372A-372F. InFIG. 3, each fan 392 directs the replacement fluid 350 into the stagnantflow area 372A-372F. Further, the fans 392 cause a back and forth flowpattern 376 in the optical cavity 370.

[0078] In FIG. 3, the flow diverters 346A-346F include three alternativetype of fans 392. More specifically, for the first and second flowdiverters 346A-346B, the entire fan 392 is positioned in the opticalcavity 370 and the motor 396 is secured to the inner wall 352 of theoptical housing 340 with a motor damper 398. The motor damper 398inhibits and dampens the reaction forces generated by the motor 396 frombeing transferred to the optical housing 340 and the optical elements342A-342G. The motor damper 398 can include a reaction mass assembly, afluid cylinder, resilient material such as a viscoelastic material, orother type of vibration damping device. Alternatively, the motor 396 canbe secured directly to the optical housing 340.

[0079] For the third and fourth flow diverters 346C-346D, for each fan392, the vanes 394 are positioned in the optical cavity 370, the outputshaft 395 extends through the optical housing 340, a seal 399 seals theoutput shaft 395 to the optical housing 340, the motor 396 is positionedoutside the optical cavity 370, and the motor 396 is secured to theouter wall 354 of the optical housing 340 with the motor damper 398. Themotor damper 398 inhibits and dampens the reaction forces generated bythe motor 396 from being transferred to the optical housing 340 and theoptical elements 342A-342G. With the motor 396 positioned outside theoptical cavity 370, the heat generated by the motor 396 is not directlytransferred to the optical cavity 370.

[0080] For the fifth and sixth flow diverters 346E-346F, for each fan392, the vanes 394 are positioned in the optical cavity 370, the outputshaft 395 extends through the optical housing 340, a seal 399 seals theoutput shaft 395 to the optical housing 340, the motor 396 is positionedoutside the optical cavity 370, and the motor 396 is secured to anotherstructure 397 that is isolated from the optical housing 340. With thisdesign, reaction forces generated by the motor 396 are not directlytransferred to the optical housing 340 and the optical elements342A-342G. With the motor 396 positioned outside the optical cavity 370,the heat generated by the motor 396 is not directly transferred to theoptical cavity 370.

[0081] The amount of amount of flow for the fan 392 can be varied. Forexample, each fan 392 can generate a flow of at least approximately 0.1liters per minute, 1 liter per minute or 10 liters per minute.

[0082] One or more of the electric fans 392 could be turned off and onat certain times so that possible vibration from the fans 392 does notinfluence the performance of the optical assembly 322. For example, theelectrical fans 392 can be turned on during the purging of the opticalassembly 322 and turned off during processing of the wafer 14(illustrated in FIG. 1).

[0083]FIG. 4A is a cross-sectional view of another embodiment of acombination 436 including an optical assembly 422 and a fluid purgingassembly 438 that are somewhat similar to the corresponding componentsdescribed above. In this embodiment, the optical assembly 422 includesoptical elements 442A-442G, element mounts 444A-444G, and flow diverters446A-446E. Further, the optical assembly 422 includes stagnant flowareas 472A-472F. However, in this embodiment, each of the flow diverters446A-446F is integrated into the element mounts 444B-444F. Further, theflow diverters 446A-446E direct the replacement fluid 450 into thestagnant flow areas 472A-472F and/or through the optical path 435.

[0084]FIG. 4B illustrates a perspective view of (i) the second elementmount 444B and second element 442B, (ii) the third element mount 444Cand the third optical element 442C, (iii) the fourth element mount 444Dand fourth element 442D, (iv) the fifth element mount 444E and fifthelement 442E, and (v) the sixth element mount 444F and the sixth element442F spaced apart along the optical axis 464. In this embodiment, thefourth and sixth element mounts 444D, 444F are similar to the secondelement mount 444B and the fifth element mount 444E is similar to thethird element mount 444C. Alternatively, each of the element mounts444B-444F can be different.

[0085] In this embodiment, the second element mount 444B is generallyflat ring shaped and extends between the inner wall 452 of the opticalhousing 440 (illustrated in FIG. 4A) and the second optical element442A. Further, the second element mount 444B encircles the secondoptical element 442A. However, in this embodiment, the second elementmount 444B includes one or more mount apertures 402 that extend throughthe second element mount 444B. In FIG. 4B, the second element mount 444Bincludes one arch shaped mount aperture 402 that is positioned on theleft side of the optical axis 464. In FIG. 4B, the fourth element mount444D and the sixth element mount 444F have a similar design.

[0086] Further, the third element mount 444C is generally flat ringshaped and extends between the inner wall 452 of the optical housing 440(illustrated in FIG. 4A) and the third optical element 442C. Further,the third element mount 444C encircles the third optical element 442C.However, in this embodiment, the third element mount 444C includes oneor more mount apertures 402 that extend through the third element mount444C. In FIG. 4B, the third element mount 444C includes one arch shapedmount aperture 402 that is positioned on the right side of the opticalaxis 464. In FIG. 4B, the fifth element mount 444E has a similar design.

[0087] In this embodiment, the mount apertures 402 of adjacent elementmounts are positioned on opposite sides of the optical axis 464.Alternatively, the mount apertures 402 can be offset approximately 90degrees or 120 degrees.

[0088] In this embodiment, the second element mount 444B defines thefirst flow deflector 446A, the third element count 444C defines thesecond flow deflector 446B, the fourth element mount 444D defines thethird flow deflector 446C, the fifth element mount 444E defines thefourth flow deflector 446D, and the sixth element mount 444F defines thefifth flow deflector 446E. The flow diverters cause a substantiallyserpentine shaped flow 476 pattern of the replacement fluid in theoptical cavity that winds between the optical elements.

[0089] Each element mount 444A-444G can be made of a number of materialsincluding metal, plastic, or other suitable materials.

[0090]FIG. 5 is a cross-sectional view of another embodiment of acombination 536 including an optical assembly 522 and a fluid purgingassembly 538 that are somewhat similar to the corresponding componentsdescribed above. In this embodiment, the optical assembly 522 includesoptical elements 542A-542G, element mounts 544A-544G, and flow diverters546A-546F. Further, the optical assembly 522 includes stagnant flowareas 572A-572F. However, in this embodiment, the flow diverters546A-546F include three vanes 580 that are similar to the vanes 280illustrated in FIG. 2B, three fans 592 similar to the fans 392illustrated in FIG. 3, and the element mounts 544A-544G with integratedflow diverters that are similar to the element mounts 444A-444Gillustrated in FIGS. 4A and 4B. Alternatively, the optical assembly 522can be designed with more or less flow diverters.

[0091] Semiconductor devices can be fabricated using the above describedsystems, by the process shown generally in FIG. 6A. In step 601 thedevice's function and performance characteristics are designed. Next, instep 602, a mask (reticle) having a pattern is designed according to theprevious designing step, and in a parallel step 603 a wafer is made froma silicon material. The mask pattern designed in step 602 is exposedonto the wafer from step 603 in step 604 by a photolithography systemdescribed hereinabove in accordance with the present invention. In step605 the semiconductor device is assembled (including the dicing process,bonding process and packaging process), finally, the device is theninspected in step 606.

[0092]FIG. 6B illustrates a detailed flowchart example of theabove-mentioned step 604 in the case of fabricating semiconductordevices. In FIG. 6B, in step 611 (oxidation step), the wafer surface isoxidized. In step 612 (CVD step), an insulation film is formed on thewafer surface. In step 613 (electrode formation step), electrodes areformed on the wafer by vapor deposition. In step 614 (ion implantationstep), ions are implanted in the wafer. The above mentioned steps611-614 form the preprocessing steps for wafers during wafer processing,and selection is made at each step according to processing requirements.

[0093] At each stage of wafer processing, when the above-mentionedpreprocessing steps have been completed, the following post-processingsteps are implemented. During post-processing, first, in step 615(photoresist formation step), photoresist is applied to a wafer. Next,in step 616 (exposure step), the above-mentioned exposure device is usedto transfer the circuit pattern of a mask (reticle) to a wafer. Then instep 617 (developing step), the exposed wafer is developed, and in step618 (etching step), parts other than residual photoresist (exposedmaterial surface) are removed by etching. In step 619 (photoresistremoval step), unnecessary photoresist remaining after etching isremoved.

[0094] Multiple circuit patterns are formed by repetition of thesepreprocessing and post-processing steps.

[0095] While the particular adjuster assembly as shown and disclosedherein is fully capable of obtaining the objects and providing theadvantages herein before stated, it is to be understood that it ismerely illustrative of the presently preferred embodiments of theinvention and that no limitations are intended to the details ofconstruction or design herein shown other than as described in theappended claims.

What is claimed is:
 1. An optical assembly for directing a beam oflight, the optical assembly for use with a replacement fluid from afluid source, the optical assembly comprising: an optical housing thatdefines an optical cavity, the optical housing including an inlet portthat is in fluid communication with the fluid source so that thereplacement fluid from the fluid source is directed into the opticalcavity and flows in the optical cavity, the optical cavity including astagnant flow area; an optical element secured to the optical housing;and a flow diverter positioned in the optical cavity, the flow diverterredirecting the flow of the replacement fluid in the optical cavity sothat the replacement fluid flows into the stagnant flow area.
 2. Theoptical assembly of claim 1 including a plurality of spaced apart flowdiverters positioned within the optical cavity, each flow diverterdiverting the flow of replacement fluid in the optical cavity.
 3. Theoptical assembly of claim 1 wherein the flow diverter is a vanepositioned in the optical cavity that causes the flow of the replacementfluid in the optical cavity to flow into the first stagnant flow area.4. The optical assembly of claim 1 wherein the flow diverter is a fanthat causes the replacement fluid in the optical cavity to flow into thestagnant flow area.
 5. The optical assembly of claim 4 wherein the fanpulls the replacement fluid into the stagnant flow area.
 6. The opticalassembly of claim 4 wherein the fan pushes the replacement fluid intothe stagnant flow area.
 7. The optical assembly of claim 1 furthercomprising an element mount that secures the optical element to theoptical housing and wherein the flow diverter is integrated into theelement mount.
 8. The optical assembly of claim 7 wherein the elementmount is generally annular ring shaped and includes a mount aperture. 9.The optical assembly of claim 1 including two element mounts that arespaced apart along an optical axis, wherein each element mount includesa mount aperture and wherein the mount aperture for one of the elementmounts is substantially opposite relative to the optical axis from themount aperture for the other element mount.
 10. The optical assembly ofclaim 9 wherein the element mounts cause a somewhat serpentine shapedflow pattern in at least a portion of the optical cavity.
 11. Theoptical assembly of claim 1 wherein the optical cavity includes aplurality of spaced apart stagnant flow areas and the optical assemblyincludes a plurality of spaced apart flow diverters positioned in theoptical cavity, each flow diverter redirecting the flow of thereplacement fluid in the optical cavity so that the replacement fluidflows into each stagnant flow area.
 12. An exposure apparatus includingan illumination source and the optical assembly of claim 1 positionednear the illumination source.
 13. A device manufactured with theapparatus according to claim
 12. 14. A wafer on which an image has beenformed by the apparatus of claim
 12. 15. A method for purging an opticalcavity of an optical assembly, the optical assembly including an opticalelement and a stagnant flow area, the method comprising the steps of:providing a fluid source of a replacement fluid; directing thereplacement fluid into the optical cavity; and redirecting the flow ofthe replacement fluid into the stagnant flow area of the optical cavitywith a flow diverter positioned in the optical cavity.
 16. The method ofclaim 15 wherein the step of redirecting includes redirecting the flowof replacement fluid with a plurality of spaced apart flow diverterspositioned within the optical cavity.
 17. The method of claim 15 whereinthe flow diverter is a vane positioned in the optical cavity that causesthe flow of the replacement fluid in the optical cavity to flow into thestagnant flow area.
 18. The method of claim 15 wherein the flow diverteris a fan that causes the replacement fluid in the optical cavity to flowinto the stagnant flow area.
 19. The method of claim 15 furthercomprising the step of securing the optical element to an opticalhousing with an element mount and wherein the flow diverter isintegrated into the element mount.
 20. The method of claim 15 whereinthe optical cavity includes a plurality of spaced apart stagnant flowareas and the step of redirecting includes the step of redirecting theflow of the replacement fluid with a plurality of spaced apart flowdiverters in the optical cavity so that the replacement fluid flows intoeach stagnant flow area.
 21. A method for making an exposure apparatusfor transferring an image from a reticle to a wafer, the methodcomprising the steps of: providing an illumination system that directsan illumination beam at the reticle; and providing an optical assemblythat is purged by the method of claim
 15. 22. A method for making anobject including at least the photolithography process, wherein thephotolithography process utilizes the apparatus made by the method ofclaim
 21. 23. A method of making a wafer utilizing the apparatus made bythe method of claim
 21. 24. A method for making an optical assembly fordirecting a beam of light, the optical assembly for use with areplacement fluid from a fluid source, the method comprising the stepsof: providing an optical housing that defines an optical cavity, theoptical cavity including a stagnant flow area; securing an opticalelement to the optical housing; directing a replacement fluid from afluid source into the optical cavity; and redirecting the replacementfluid into the stagnant flow area with a fluid diverter positionedwithin the optical cavity.
 25. The method of claim 24 wherein the stepof redirecting includes redirecting the flow of replacement fluid with aplurality of spaced apart flow diverters positioned within the opticalcavity.
 26. The method of claim 24 wherein the flow diverter is a vanepositioned in the optical cavity that causes the flow of the replacementfluid in the optical cavity to flow into the stagnant flow area.
 27. Themethod of claim 25 wherein the flow diverter is a fan that causes thereplacement fluid in the optical cavity to flow into the stagnant flowarea.
 28. The method of claim 24 further comprising the step of securingthe optical element to the optical housing with an element mount andwherein the flow diverter is integrated into the element mount.
 29. Themethod of claim 24 wherein the optical cavity includes a plurality ofspaced apart stagnant flow areas and the step of redirecting includesthe step of redirecting the flow of the replacement fluid with aplurality of spaced apart flow diverters in the optical cavity so thatthe replacement fluid flows into each stagnant flow area.
 30. A methodfor making an exposure apparatus for transferring an image from areticle to a wafer, the method comprising the steps of: providing anillumination system that directs an illumination beam at the reticle;and providing an optical assembly made by the method of claim
 24. 31. Amethod for making an object including at least the photolithographyprocess, wherein the photolithography process utilizes the apparatusmade by the method of claim
 30. 32. A method of making a wafer utilizingthe apparatus made by the method of claim 30.